1. Field of the Invention
The present invention relates to a current control apparatus in a switched reluctance motor (SRM), and more particularly to a current control apparatus in a switched reluctance motor (SRM) which searches for a current error by comparing a current controlling signal commanded by a current command unit with a current actually applied to the SRM and then operates the SRM by a current adjacent to the command current by compensating a current value corresponding to the compared current error, thereby reducing a noise caused by a torque ripple when rotating the motor and enhancing the efficiency of the motor.
2. Description of the Related Art
Generally, a switched reluctance motor (SRM) is a kind of a reluctance motor which mainly includes: a polyphase stator which generates a magnetic force by binding an armature coil; a rotor which is rotated by a magnetic attractive force generated according to relative positions of a tooth and the magnetic force generated by the stator; and a position detecting unit which has a position detection sensing unit and a sensing plate and detects the position of the rotor by sensing a position detecting pulse by a resolution of a predetermined angle as the position of the rotor varies. Here, a plurality of teeth are symmetrically formed at the rotor, and the armature coil symmetrically binds each of the polyphase stator. The position detection sensing unit outputs the position detection pulse by detecting the position of the rotor and synchronizes with the position detection pulse, thereby successively driving the polyphase armature coils.
The power supplied to the armature coil which is bound to the polyphase stator is controlled by a switching element. At this time, by successively varying the excitation state between the rotor and the stator as the input pulse signal is applied to a controlling terminal of the switching element by synchronizing with the position detection pulse of the position detecting unit, a forward rotating torque corresponding to the input pulse signal can be generated at the rotor by the magnetic attractive force. Moreover, in the case that a specific excitation state is not varied, it is possible to stop the rotor at a predetermined position. In addition, by controlling the phase of the inputted pulse signal which is applied to the switching element based on the position where the inductance reaches at its maximum, an inverse rotating force can be generated. As described above, it is possible to widely apply the control operation in the various directions to the washing machine, etc.
At this time, to successively vary the excitation state of each phase, it is essential to sense the position of the rotor.
There are many prior arts which have been disclosed relating to the SRM, such as U.S. Pat. No. 4,748,387, "DC brushless motor driving method and apparatus for accurately controlling starting position of rotor" patented on May 1988; U.S. Pat. No. 4,990,843, "Reluctance motor" patented on February 1991; U.S. Pat. No. 5,111,095, "Polyphase switched reluctance motor" patented on May 1992; U.S. Pat. No. 5,461,295, "Noise reduction in a switched reluctance motor by current profile manipulation" patented on October 1995; and U.S. Pat. No. 5,539,293, "Rotor position encoder having features in decodable angular position" patented on July 1996.
FIG. 1 is an illustrative view showing the inner structure of the conventional SRM. It illustrates a SRM having three phases of A, B and C.
In the conventional SRM 1, an armature coil L binds the core of the stator 3 located around the rotor 2. The torque can be generated by the magnetic attractive force functioning between the rotor 2 and the core of the stator 3 magnetized when electrifying the armature coil L. By successively electrifying the armature coil L of each A, B and C phase, it is possible to have a structure capable of rotating the rotor 2 to a desired direction.
Moreover, inside of the conventional SRM 1, as shown in FIG. 2, a sensor plate 7 in which a plurality of slits 6 are formed along the concentric circumference is connected to the rotor 2. An optical sensor (not illustrated) having a light-emitting element and a light receiving element is located facing the slit 6. Accordingly, the light transmitted from the light-emitting element is transmitted through the slit 6 of the sensor plate 7 and then is incident upon the light receiving element, and thereby a predetermined detection pulse is generated. As a result, it is possible to detect the position of the rotor.
As described above, it is possible to generate the forward rotating torque or the reverse rotating torque by controlling the switching pulse applied to an inverter unit, which will be illustrated, according to the location of the detected rotor 2. Moreover, in the case that any specific excitation state is not varied, it is possible to stop the rotor at a predetermined position.
FIG. 3 is a wave form illustrating the inductance according to the relative position of the rotor 2 and the core out of a plurality of cores of the stator 3. Here, the waveform of the electrifying signal is formed when the rotor 2 shown in FIG. 1 is rotated in the direction of the arrow.
As shown in FIG. 3, as the rotor 2 approaches to a core having any phase out of the cores of stator 3, the inductance L increases. When the rotor 2 is aligned with a core of any phase, the inductance L reaches at its maximum. In addition, as the rotor 2 is located apart from a core having an any phase, the inductance L decreases. Conventionally, it is designed that the switching pulse can be evenly outputted at a position which is advanced as much as 0-7.5 degrees based on the time when the inductance L increases, irrelevantly to the rotating speed.
Due to the above-mentioned operating characteristic, it is recognized that the SRM is very environment-resistant and can generate a high torque at a high speed as it has no rectification limit. Moreover, as there is no brush in the SRM, it is easy to repair. However, in the case that the controlling the phase current using the switching pulse is inaccurate, the operating characteristic of the SRM is extremely degenerated.
Main factors which hinder the exact control of the phase current will be explained. As a current error between the current controlling signal which is commanded by the current command unit and the current which is actually applied to the SRM exceeds the allowable value and the current error is accumulated and spread, the SRM does not operate normally or the uneven rotating torque can be generated. Accordingly, as the current controlling apparatus of the conventional SRM cannot remove or compensate effectively the error current which is accumulated and spread, the rotating torque is degenerated and the noise is generated, thereby resulting in degenerating the entire efficiency of the SRM.